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Middle-aged people with diets high in animal protein, such as meat, poultry, eggs, milk and cheese, face a dramatically increased risk of dying from cancer compared with those who eat low animal protein diets, according to a University of Southern California study published Tuesday in the journal Cell Metabolism.

The study found 50-65-year-olds who consumed a "high-protein" diet - meaning they got 20 percent or more of their calories from animal protein - were four times more likely to die from cancer, compared with those who consumed less than 10 percent of their daily calories in animal protein. A press release accompanying the study called that "a mortality risk factor comparable to smoking."

The risk of early death from all causes soared by 74 percent among the high-protein consumers, researchers found.

But the picture changes for those over 65. For them, it appears that a moderate-to-high protein diet actually reduces cancer and overall mortality, and is helpful in preventing age-dependent weight loss and malnourishment.

Researchers focused their study on a national cross-section of 6,381 people 50 and older who were tracked for nearly 20 years.

They also found that among all the age groups studied, a diet high in animal protein increases insulin production and the risk of dying from diabetes-related causes.

The higher risk of cancer and overall death among the middle aged and the increase in diabetes deaths were "either abolished or attenuated if the proteins were plant derived," the study said.

Various health agencies recommend that daily intake of animal protein should be about .8 grams per kilogram. So a 130-pound adult should eat between 45 and 50 grams of animal protein per day. A 160-pound adult should eat between 60 and 65 grams per day. How much protein is that? This will help you calculate: